Wafer transport systems configured for use in semiconductor wafer-level processing typically include a stage having a chuck that secures the wafer for processing. Sometimes the stage is stationary, and sometimes it is moveable. Some applications require that the stage move linearly in one, two, or three Cartesian dimensions, with or without rotation. The speed of the stage motion can dictate the throughput of the entire wafer processing platform if a significant amount of the total process time is spent aligning and transporting the wafer.
For applications including optical processing, a moveable optics assembly can be mounted above the wafer surface, thereby minimizing the wafer transport distances required. The primary direction of stage motion is referred to as the “major axis,” and the direction of stage motion perpendicular to the primary direction is referred to as the “minor axis.” The chuck holding the wafer, or specimen, to be processed may be mounted to a major axis stage for movement along the major axis, a minor axis stage for movement along the minor axis, or in stationary position below the major and minor axes. The major axis stage may support the minor axis stage, or they may be independent of each other.
Stage design of such optical systems is becoming more critical as electrical circuit dimensions shrink. One stage design consideration is the impact of process quality stemming from vibrational and thermal stability of the wafer chuck and optics assembly. In the case in which the laser beam position is continually adjusted, state-of-the-art structures supporting the laser assembly are too flexible to maintain the required level of precision. Moreover, as circuit dimensions shrink, particle contamination becomes of greater concern.